Abstract: A data migration system that enables a database system to migrate from a network data model to a relational data model in a short development time, without degradation in data integrity. A record migration unit creates target records for the relational data model. The records are arranged in the same way as they originally were in the network data model before data migration has been made. A primary key addition unit then adds a primary key to each of the target records so that they can be uniquely identified. To preserve the original parent-child relationships between records, a relation key addition unit selects each child record from among the target records, identifies the parent of the child record by referring to the pointers added to corresponding source records, and gives a value of the primary key of the parent record to the child record as a relation key thereof.